The pneumatic conveying of various materials has begun to achieve wide acceptance in the art of materials handling, particularly since it is possible to efficiently convey a wide variety of materials in substantially completely closed systems in an economic manner, and where significant, with minimum risk of explosion or fire otherwise due to mechanically induced electrostatic charges or electrical discharges which occasionally result when electrical control systems are utilized.
The essential component in such pneumatically operated systems generally consists of a hopper and/or feeder which delivers material from a remote source through the hopper and/or feeder to a point of consumption of the material being conveyed by means of a partial vacuum generated by pneumatically operated vacuum producing devices actuated by high pressure air from a central source or individual air compressors, a particularly useful device being a venturi power unit which produces a substantial vacuum upon passage of high pressure air through the venturi tube.
Conventional hoppers, which are utilized for the conveyance of a wide variety of materials, generally consist of an upright cylindrical body having an inverted conical lower portion depending therefrom and terminating in a much smaller discharge port which may be actuated by a variety of discharge valve mechanisms. Such hoppers are utilized in all types of systems, including pneumatically actuated systems.
While the conventional form of hopper is quite satisfactory for the conveyance of many materials, serious difficulties are frequently encountered with certain materials which tend to bridge in the conical portion of the hopper leading to the discharge valve. For example, very bulky materials, such as bottle caps, corks, balls of nylon waste and moist or hygroscopic materials, and the like, will almost invariably cause bridging problems in conventional conical hoppers, resulting in significant shut-down time and possible loss of at least some of the material being conveyed.
While the use of external vibratory mechanisms tends to alleviate this problem to some degree, such devices have not proved to be a complete solution to the problem caused by the restrictive conical hopper configuration in relation to the type of material being conveyed. Mechanical agitation of the hopper contents is also utilized, but this results in mechanically complicated and expensive equipment.
Similar bridging problems are encountered with dry, dusty materials, especially those which are finely divided and highly dense, or bulky and yet very dusty. Such materials add a further complication if they are to be pneumatically conveyed, since the conventional wide-mouthed conical hopper suffers from the limitations inherent in the conical discharge portion; yet a straight-walled tubular hopper may not provide a sufficiently large enough area to introduce adequate capacity for efficient screening of the dust from the vacuum system as required.